These studies involve recording action potentials from single neurons and slow waves in the septal nuclei, hippocampal formation and retrohippocampal areas of behaving rats. The rats will have multiple recording electrodes, and many will have electrodes to electrically stimulate parts of the limbic system. On these rats three experiments will be done. 1) Phase relations of the action potentials of neurons to the slow wave theta rhythm will be determined in the three areas studied. By using the same reference for recording hippocampal slow wave theta rhythm the temporal relation of the firing of neurons to each other can be determined. These data are also necessary to interpret the mechanisms generating the slow wave theta. 2) The extracellular electrophysiology of behaviorally identified cells can be studied during a controlled behavior. 3) The changes in the electrophysiology of a cell can be studied in different behaviors. In most cases, all three experiments will be formed simultaneously in the same rat. The first and second experiments are primarily directed toward understanding the cellular mechanisms of generation of the hippocampal slow wave theta rhythm. The third experiment is directed toward an understanding of the cellular consequences of the slow wave theta rhythm in the hippocampus. These cellular consequences, however, are important data for the analysis of the cellular mechanisms, and vice versa. The cellular consequences of the theta rhythm also tell us something about how information processing in the hippocampus varies in different behaviors.